The Congress for New Urbanism recently held a competition to explain just what the connection is between urban planning and the environment–and if you’re fuzzy on the issue, you need to watch the winning video, created by John Paget:

Sobering stuff, which makes a lot of sense: Wouldn’t it be great to replace car commutes with walkable town centers? But what the video elides is that many cities actually makes this sort of development illegal, with zoning regulations that actively discourage “mixed use” planning. And many sprawling cities don’t have any control over their own borders–developers frequently find it cheaper to simply move further out, rather that work within existing planning frameworks.

The bottom line: Greener cities aren’t about crazy vertical farms and houses with solar panels. They’re about zoning codes–subtle rules on a sheet of paper that determine the very fabric of a city for decades at a time. You can build all the hybrids you want–it doesn’t matter if suburbia still continues to grow. That’s why the best urban planning firms don’t take architecture as a starting point–they begin by reworking existing zoning laws. One firm is Dover Kohl, based in Memphis, Tennessee. Sure, they build nice little mixed-use developments. But they’ve also done extensive work in “retrofitting” suburbia–taking existing buildings and tweaking codes to fill-in sprawl and encourage long-term density. That’s where the real heavy lifting is, in architecture and urban planning: Working with officials and community boards and citizens, trying to figure out how you write the blueprint for a community that can grow in the long term.